Nowadays, the increase in transmission traffic is increasing demands for large capacity optical transmission systems. In wavelength division multiplexing (WDM), in order to increase the transmission capacity per wavelength, multiple phase shift keying and digital coherent receivers have been introduced, and 100-Gbps-per-wavelength class optical transmission technologies have been developed.
From a viewpoint different from an increase in the transmission capacity per wavelength, optical transmission technologies using multicore fibers are attracting attention as technologies with which the transmission capacity per optical fiber is increased.
Generally, an optical fiber has a single core therein and signal light is transmitted through the single core. A multicore fiber has a plurality of cores in an optical fiber and signal light is transmitted through the plurality of cores. This may increase the transmission capacity per optical fiber as many times as the number of cores.
As related art, optical amplification technologies using multicore fibers have been proposed. One of related-art technologies is, for example, discussed in Japanese Laid-open Patent Publication No. 2-002533.
However, with a related-art optical fiber amplifier that amplifies light using a multicore fiber, excitation is performed in each of the cores. Thus, pump light sources are usually provided as many as the number of cores of the multicores. This increases the number of components of the optical fiber amplifier and the size of the optical fiber amplifier, thereby increasing the size of the circuitry.